The anatomic site of photodynamic therapy is a determinant for immunosuppression in a murine model

The role of the irradiation site in the induction of suppression of the contact hypersensitivity (CHS) response following photodynamic therapy (PDT) was examined in a murine model. Laser irradiation on the flanks of nontumor-bearing Photofrin-injected mice caused suppression of the CHS response. If the irradiation was conducted on a subcutaneously implanted foil disc on the flank no immunosuppression occurred, indicating that no suppressive factor(s) of sufficient quantity to cause suppression was released from the skin, but rather irradiation of internal organs was the cause. Irradiation of tumors implanted on the flanks of mice reduced the suppression, suggesting an immunopotentiating effect of PDT. Irradiation on the thigh in the presence or absence of a tumor gave no immunosuppression. These results suggest that the anatomic site of irradiation is one determinant for the elicitation of suppression of the CHS response.     

IL-10 does not play a role in cutaneous Photofrin photodynamic therapy-induced suppression of the contact hypersensitivity response.

Photodynamic therapy (PDT) treatment of both malignant and benign skin diseases has proven to be effective, and its use is increasing worldwide. However, preclinical studies using murine models have shown that PDT of the skin inhibits cell-mediated immune reactions, as measured by the suppression of the contact hypersensitivity (CHS) reaction. We have previously demonstrated that PDT enhances IL-10 expression in treated skin, and that the kinetics of induction of IL-10 is similar to the kinetics of suppression of systemic CHS reactions by cutaneous PDT. In the following report we have expanded upon these studies to demonstrate that cutaneous PDT, using Photofrin, induces elevated levels of systemic IL-10 that persist for at least 28 days following treatment. The increase in systemic IL-10 correlates to a prolonged suppression of CHS of at least 28 days following cutaneous PDT. IL-10 has been implicated as the causative agent in the suppression of cell-mediated immune reactions by UVB and transdermal PDT. However, in the studies reported here we demonstrate that the suppression of CHS by cutaneous PDT occurs via an IL-10 independent mechanism, as administration of anti-IL-10 antibodies had no effect on the ability of PDT to induce CHS suppression. These results were further confirmed using IL-10 knockout (KO) mice. Cutaneous PDT of IL-10 KO mice resulted in CHS suppression that was not significantly different from suppression induced in wild-type mice. Thus, it appears as though IL-10 does not play a role in CHS suppression by cutaneous PDT. Suppression of cell-mediated immune reactions by UVB and transdermal PDT is reversible by IL-12, which is critical for the development of these reactions. We show that administration of exogenous IL-12 is also able to reverse CHS suppression induced by cutaneous PDT, suggesting that whereas suppression of cell-mediated immune reactions by UVB, transdermal PDT and cutaneous PDT occurs via different mechanisms, a common regulatory point exists.     

Platelet-activating factor does not mediate UVB-induced local immune suppression

The lipid mediator Platelet-activating factor (PAF) and oxidized glycerophosphocholine PAF agonists produced by UVB have been demonstrated to play a pivotal role in UVB-mediated systemic immunosuppression. Importantly, employing the ability of distant UVB irradiation to inhibit contact hypersensitivity (CHS) responses to the chemical antigen dinitrofluorobenzene (DNFB) to an area of unirradiated murine skin, we and others have demonstrated that UVB-mediated systemic immunosuppression was only observed in PAF-R expressing wild type (WT) mice and not in PAF-R-knockout (Pafr-/-) mice. As it is not known if PAF is involved in UVB-mediated local immunosuppression, these studies compared local UVB on CHS responses in WT versus Pafr-/- mice. We demonstrate that the application of DNFB onto UVB-exposed (locally) area of mouse skin resulted in a similar significant inhibition of subsequent CHS responses in both WT and Pafr-/- mice compared to sham-irradiated control mice. Furthermore, the expression of langerin, a marker for the presence of Langerhans cells was substantially reduced equally in the epidermal ears of UVB-irradiated WT and Pafr-/- mice compared to their respective sham control groups. These findings indicate that the PAF-R is not involved UVB-induced local immunosuppression.     

SYSTEMIC IMMUNOSUPPRESSION INDUCED BY PHOTODYNAMIC THERAPY (PDT) IS ADOPTIVELY TRANSFERRED BY MACROPHAGES

Some derivatives of hematoporphyrins are strongly retained by tumor tissue as compared to normal tissue, and exposure of these photosensitizers to radiation in the visible spectrum can cause serious biological damage. These properties have been exploited in the development of a new treatment for cancer termed photodynamic therapy (PDT). However, recent studies have also demonstrated that PDT can also induce a state of systemic immunosuppression. The purpose of this study was to determine whether PDT-induced suppression of contact hypersensitivity (CHS) responses was an active phenomenon that could be adoptively transferred by viable splenocytes from PDT-treated mice. Although induction of adoptively transferable suppressor cells in PDT-treated mice required exposure to antigen, the suppressor cells were found to be antigen nonspecific in their function. Furthermore, splenocytes from PDT-treated mice were capable of generating levels of allospecific cytotoxic T lymphocyte (CTL) activity which were comparable to those generated by normal control mice, but the ability of irradiated spleen cells from PDT-treated mice to stimulate a mixed lymphocyte response (MLR) was dramatically impaired. Finally, chromatographic separation of T cells, B cells and macrophages showed that the cell type which mediates adoptively transferable suppression of CHS responsiveness is in the macrophage lineage.     

Characteristics of the immunosuppression induced by cutaneous photodynamic therapy: persistence, antigen specificity and cell type involved

Relatively little is known about the immunosuppression induced in mice which have received cutaneous photodynamic therapy (PDT). Consequently, experiments were undertaken using mice which received dorsal PDT using Photofrin as the photosensitizer in an attempt to characterize the overall nature of the immunosuppression. Photoirradiation of mice at various times after injection indicated there was no correlation between photosensitivity and immunosuppression. The suppression was found to be adoptively transferable and antigen specific suggesting the generation of suppressor cells. Selective cell depletions prior to adoptive transfer indicated a CD4+ T cell to be responsible for the immunosuppression. Interestingly, using allogeneic spleen cells, no effect on the delayed type hypersensitivity (DTH) response was found. The results indicate that the suppression induced by cutaneous PDT, with the exception of the lack of DTH suppression, is similar to that induced by UVB irradiation but unlike that reported using laser PDT of the peritoneal cavity. This suggests that not only the type of photoirradiation but also the site of photoirradiation might determine the character of the induced immunosuppression.     

Immunosuppressive Effects of Silicon Phthalocyanine Photodynamic Therapy

The purpose of this study was to determine if silicon phthalocyanine 4 (Pc 4), a second-generation photosensitizer being evaluated for the photodynamic therapy (PDT) of solid tumors, was immunosuppressive. Mice treated with Pc 4 PDT 3 days before dinitrofluorobenzene sensitization showed significant suppression of their cell-mediated immune response when compared to mice that were not exposed to PDT. The response was dose dependent, required both Pc 4 and light and occurred at a skin site remote from that exposed to the laser. The immunosuppression could not be reversed by in vivo pre-treatment of mice with antibodies to tumor necrosis factor-alpha or interleukin-10. These results provide evidence that induction of cell-mediated immunity is suppressed after Pc 4 PDT. Strategies that prevent PDT-mediated immunosuppression may therefore enhance the efficacy of this therapeutic modality.     

Suppression of Different Phases of Systemic Contact Hypersensitivity by Urocanic Acid Oxidation Productsfn1

On exposure to UV‐B, the epidermal component trans‐urocanic acid (UCA) is not only photoisomerized into cis‐ UCA but will also, at least in part, be photooxidized into UCA oxidation products (UOPs). We hypothesized that UOPs can mimic UV‐induced systemic immunosuppression comparable to the suppressive properties already established for cis‐UCA. A crude mixture of UOPs showed a significant suppression of the sensitization phase of the systemic contact hypersensitivity (CHS) response to picryl chloride (PCI). Three of the UOPs were selected for this study: imidazole‐4‐carboxylic acid (ImCOOH), immidazole‐4‐carboxaldehyde (ImCHO) and imidazole‐4‐acetic acid (ImAc). Effects on the sensitization, elicitation and postelicitation phases of CHS to PCI in BALB/c mice were studied and compared with the effects of cis‐UCA. ImCHO was equally effective at suppressing the sensitization phase as cis‐UCA. The triplet combination of the imidazoles (1:1:1) showed more pronounced suppression than that induced by cis‐UCA. The most effective compounds for the suppression of the elicitation phase appeared to be ImAc and cis‐UCA. Significant suppression of the postelicitation phase was only obtained with the triplet combination of ImCHO, ImCOOH and ImAc, the combination that appeared to be effective at all three tested phases. Because these three UOPs are present in UV‐B‐exposed human stratum corvneum, these compounds may play a role in UV‐B‐induced immunosuppression.     

The effect of a vitamin A acetate diet on ultraviolet radiation-induced immune suppression as measured by contact hypersensitivity in mice

The adverse health effects caused by increased exposure to ultraviolet radiation (UVR) due to deterioration of stratospheric ozone are of major concern. These health effects include sunburn, skin cancer, cataracts and immune suppression. Immune suppression has been associated with the release of cytokines, a defect in antigen presentation, induction of suppressor T cells and suppression of contact hypersensitivity (CH). CH is typically assessed by the mouse ear swelling test (MEST). Previous studies have demonstrated enhanced CH responses with vitamin A acetate (VAA) dietary supplementation assessed by MEST and the local lymph node assay (LLNA). To determine the effect that VAA has on UVR-induced immune suppression, we examined both the induction and elicitation phases of CH using murine models. The MEST was used to evaluate the interaction of UVR and VAA on CH elicitation. However, a positive MEST response requires that the induction phase as well as the elicitation phase of CH be functional. The LLNA was used to evaluate the interaction of UVR and VAA only on CH induction. We tested the hypothesis that mice maintained on a VAA-enriched diet are more resistant to UVR-induced immune suppression (CH) than those maintained on a control diet. Mice were maintained on a VAA-enriched or the control diet for 3 weeks and then exposed to UVR 3 days prior to sensitization with 2,4-dinitrofluorobenzene (DNFB). VAA enhanced the MEST response in both UVR-exposed and non-UVR-exposed mice. The VAA-enriched diet did not significantly alter the LLNA response in either UVR- or non-UVR-exposed mice. However, there was significant suppression in CH by UVR as measured by the LLNA. These results indicate that (1) the VAA-enriched diet does not restore the number of proliferating cells in the CH induction phase of UVR-induced immunosuppression; (2) the immunosuppressive effects of UVR affect the induction phase of CH; and (3) the LLNA should be examined as an alternative to the MEST for measurement of UVR-induced immunosuppression. The data indicate that the VAA-enriched diet enhanced the elicitation response (MEST) but not the earlier induction phase (LLNA). Further studies are necessary to define mechanisms of action, but modulation of cytokines and effects of specific lymphocyte subsets, as well as systemic effects and local modulation at the site of elicitation are possible. Additionally, future studies to evaluate the effect of the VAA-enriched diet when multiple doses of both UVR and DNFB are used would be of interest for both the LLNA and MEST end-points.     

No adaptation to UV-induced immunosuppression and DNA damage following exposure of mice to chronic UV-exposure

It is well known that ultraviolet (UV) radiation induces erythema, immunosuppression and carcinogenesis. We hypothesized that chronic exposure to solar UV radiation induces adaptation that eventually prevents the suppression of acquired immunity. We studied adaptation for UV-induced immunosuppression after chronic exposure of mice to a suberythemal dose of solar simulated radiation (SSR) with Cleo Natural lamps, and subsequent exposure to an immunosuppressive dose of solar or UVB radiation (TL12). After UV dosing, the mice were sensitized and challenged with either diphenylcyclopropenone (DPCP) or picryl chloride (PCl). To assess the adaptation induced by solar simulated radiation, we measured the proliferative response and cytokine production of skin-draining lymph node cells after immunization to DPCP, the contact hypersensitivity (CHS) response to PCl, and thymine-thymine (T-T) cyclobutane dimers in the skin of mice. After induction of immunosuppression by SSR or by TL12 lamps, the proliferative response of draining lymph node cells after challenge with DPCP, or the CHS after challenge with PCl, showed significant suppression of the immune response. Chronic irradiation from SSR preceding the immunosuppressive dose of UV failed to restore the suppressed immune response. Reduced lipopolysaccharide-triggered cytokine production (of IL-12p40, IFN-gamma, IL-6 and TNF-alpha) by draining lymph node cells of mice sensitized and challenged with DPCP indicated that no adaptation is induced. In addition, the mice were not protected from T-T dimer DNA damage after chronic solar irradiation. Our studies reveal no evidence that chronic exposure to low doses of SSR induces adaptation to UV-induced suppression of acquired immunity.     

SUPPRESSION OF CONTACT HYPERSENSITIVITY BY UV RADIATION AND ITS RELATIONSHIP TO UV-INDUCED SUPPRESSION OF TUMOR IMMUNITY

Abstract— In this study, we examine some of the photobiologic and immunologic characteristics of the suppression of contact hypersensitivity (CHS) by UV radiation. BALB/c mice were irradiated on the shaved dorsal skin with FS40 sunlamps and sensitized 5 days later by applying a contact sensitizer lo the shaved abdomen. The suppression of CHS resulting from exposure to a given total dose of UV radiation was unaffected by changes in dose fractionation over a 5-day period and by changes in dose-rate over a 10-fold range. Elimination of wavelengths below 315 nm with a mylar filter abrogated the suppressive effect of the sunlamps, even when the same total energy was administered. Irradiation of unshaved mice required 14 times more energy to produce 50% suppression than was required for shaved mice, suggesting that the exposed skin is the primary target of this effect. Contact sensitization of UV-irradiated, but not unirradiated, mice induced the appearance of antigen-specific suppressor T lymphocytes in their spleen. The photobiologic and immunologic similarities between the suppression of CHS by UV radiation and the UV-mediated suppression of tumor rejection that we described previously suggest that these two immunosuppressive effects of UV exposure share certain steps in their pathways.     

Activation of the IL-10 gene promoter following photodynamic therapy of murine keratinocytes

Photodynamic therapy (PDT), an anticancer treatment modality, has recently been shown to be an effective treatment for several autoimmune disease models including antigen-induced arthritis. PDT was found to induce the expression of IL-10 messenger RNA (mRNA) and protein in the skin, and this expression has similar kinetics to the appearance of PDT-induced suppression of skin-mediated immune responses such as the contract hypersensitivity (CHS) response. Some aspects of the UVB-induced suppression of the immune response have been linked to the induction of IL-10. IL-10 has been shown to inhibit the development and activation of Th1 cells, which are critical for many cell-mediated immune responses, including CHS. We have examined the effect of PDT and UVB irradiation on the activity of the IL-10 gene promoter and on IL-10 mRNA stability using the murine keratinocyte line, PAM 212. In vitro PDT induces IL-10 mRNA and protein expression from PAM 212 cells, which can be correlated with an increase in AP-1 DNA binding activity and activation of the IL-10 gene promoter by PDT. Deletion of an AP-1 response element from the IL-10 gene promoter was shown to abrogate the PDT-induced promoter activity indicating that the AP-1 response element is critical to IL-10 induction by PDT. In addition, PDT results in an increase in IL-10 mRNA stability, which may also contribute to the increased IL-10 expression in PAM 212 cells following PDT. In vitro UVB irradiation also results in activation of the IL-10 promoter. However, in contrast to PDT, UVB-induced activation of the IL-10 promoter is not AP-1 dependent and did not increase IL-10 mRNA stability.     

Interaction of UVB-absorbing sunscreen ingredients with cutaneous molecules may alter photoimmune protection.

Studies of the photoimmunoprotective properties of sunscreens have produced disparate results. In this study in hairless mice, we compared two UVB absorbers, 2-ethylhexyl-p-methoxycinnamate (2-EHMC) and octyl-N-dimethyl-p-aminobenzoate (o-PABA), individually formulated in a common base lotion with a sunburn protection factor of 6. We measured their capacity to protect against suppression of the contact hypersensitivity (CHS) induced by three daily exposures of the dorsum to 6x the minimal erythemal/edematous dose (MED) of solar-simulated UV radiation (SSUV), in comparison with base lotion-treated mice exposed to 3 x 1 MED of SSUV. All treatments produced a similar minimal erythema. CHS was equally suppressed in mice irradiated through o-PABA and base lotion, but the suppression was significantly reduced in mice irradiated through 2-EHMC. Neither UVB absorber inhibited the epidermal photoisomerization to the immunosuppressive mediator, cis-urocanic acid. However, when mice were treated with exogenous cis-urocanic acid topically on the dorsum, but not when injected subcutaneously on the abdomen, suppression of CHS was observed in o-PABA- and base lotion-treated mice, but not in 2-EHMC-treated mice. Thus, the enhanced immunoprotection in mice irradiated through 2-EHMC apparently resulted from the direct inactivation of epidermal cis-urocanic acid by 2-EHMC. We conclude that comparative assessment of photoimmunoprotection by UV absorbers requires SSUV, erythemally matched exposures and consideration of potential interactions with cutaneous molecules.     

PROTECTION AGAINST ULTRAVIOLET-B RADIATION-INDUCED LOCAL and SYSTEMIC SUPPRESSION OF CONTACT HYPERSENSITIVITY and EDEMA RESPONSES IN C3H/HeN MICE BY GREEN TEA POLYPHENOLS

Abstract— Exposure of skin to UV radiation can cause diverse biological effects, including induction of inflammation, alteration in cutaneous immune cells and impairment of contact hypersensitivity (CHS) responses. Our laboratory has demonstrated that oral feeding as well as topical application of a poly-phenolic fraction isolated from green tea (GTP) affords protection against the carcinogenic effects of UVB (280–320 nm) radiation. In this study, we investigated whether GTP could protect against UVB-induced immunosuppression and cutaneous inflammatory responses in C3H mice. Immunosuppression was assessed by contact sensitization with 2,4-dinitrofluorobenzene applied to UVB-irradiated skin (local suppression) or to a distant site (systemic suppression), while double skin-fold swelling was used as the measure of UVB-induced inflammation. Topical application of GTP (1–6 mg/animal), 30 min prior to or 30 min after exposure to a single dose of UVB (2 kj/m²) resulted in significant protection against local (25–90%) and systemic suppression (23–95%) of CHS and inflammation in mouse dorsal skin (70–80%). These protective effects were dependent on the dose of GTP employed; increasing the dose (1–6 mg/animal) resulted in an increased protective effect (25–93%). The protective effects were also dependent on the dose of UVB (2–32 kJ/m²). Among the four major epicatechin derivatives present in GTP, (‐)-epigallocatechin-3-gallate, the major constituent in GTP, was found to be the most effective in affording protection against UVB-caused CHS and inflammatory responses. Our study suggests that green tea, specifically polyphenols present therein, may be useful against inflammatory dermatoses and immunosuppression caused by solar radiation.     

SUPPRESSION OF THE INDUCTION OF DELAYED-TYPE HYPERSENSITIVITY REACTIONS IN MICE BY A SINGLE EXPOSURE TO ULTRAVIOLET RADIATION

Abstract— After a single exposure of mice to UV radiation, their ability to generate a contact hypersensitivity (CHS) response to contact sensitizers applied epicutaneously to distant, unirradiated skin is severely impaired. It is not clear, however, if the classic delayed type hypersensitivity (DTH) reponse to exogenous antigens, injected into the subcutaneous (s.c.) space, can also be modulated by UV radiation. We report here that a single exposure of mice to UV radiation suppressed the induction of DTH to both erythrocyte and soluble protein antigens injected s.c., but did not suppress the elicitation of the response. The suppressive effect was abrogated by cyclophosphamide treatment. In addition, antigen-specific suppressor cells were found in the spleens of the mice with a decreased DTH response. Since the ability to mount a DTH response has been linked with the resistance to certain pathogenic microorganisms, we suggest that the suppression of DTH by UV radiation may have the potential to compromise host resistance to such infectious agents.     

AN ANIMAL MODEL AND NEW PHOTOSENSITIZERS FOR PHOTOPHERESIS

Recently, photopheresis was introduced as a therapy for several T cell-mediated disorders. The treatment results in a specific immune response against the pathogenic clone of T cells involved. However, although promising there is controversy concerning the use of photopheresis in some diseases, e.g . systemic sclerosis. One of the problems is that there is not yet sufficient insight into the mechanism underlying the therapy. This lack of knowledge is partly caused by the fact that there are no easy-to-handle animal models available for photopheresis.
This report describes such a model—a Wistar-derived rat with contact hypersensitivity (CHS); a T cell-mediated immune response. White blood cells from CHS rats were simultaneously exposed to 8-methoxypsoralen (8-MOP) and ultraviolet A radiation (UVA) and subsequently intravenously injected into other syngeneic rats suffering from the same disorder. This treatment appears to be very efficacious in suppressing the immunological response against the applied contact allergen, 2,4-dinitroAuorobenzene (DNFB). In addition, the generated suppression of CHS is highly specific and transferable. Furthermore, drugs other than 8-MOP (chlordiazepoxide, nitrofurantoin and chlor-promazine) also appear to be active in our model.     

The immunosuppressive effects of phthalocyanine photodynamic therapy in mice are mediated by CD4+ and CD8+ T cells and can be adoptively transferred to naive recipients

Photodynamic therapy (PDT) is a promising treatment modality for malignant tumors but it is also immunosuppressive which may reduce its therapeutic efficacy. The purpose of our study was to elucidate the role of CD4+ and CD8+ T cells in PDT immunosuppression. Using silicon phthalocyanine 4 (Pc4) as photosensitizer, nontumor-bearing CD4 knockout (CD4-/-) mice and their wild type (WT) counterparts were subjected to Pc4-PDT in a manner identical to that used for tumor regression (1 cm spot size, 0.5 mg kg(-1) Pc4, 110 J cm(-2) light) to assess the effect of Pc4-PDT on cell-mediated immunity. There was a decrease in immunosuppression in CD4-/- mice compared with WT mice. We next examined the role of CD8+ T cells in Pc4-PDT-induced immunosuppression using CD8-/- mice following the same treatment regimen used for CD4-/- mice. Similar to CD4-/- mice, CD8-/- mice exhibited less immunosuppression than WT mice. Pc4-PDT-induced immunosuppression could be adoptively transferred with spleen cells from Pc4-PDT treated donor mice to syngenic naive recipients (P < 0.05) and was mediated primarily by T cells, although macrophages were also found to play a role. Procedures that limit PDT-induced immunosuppression but do not affect PDT-induced regression of tumors may prove superior to PDT alone in promoting long-term antitumor responses.     

Chronic Low-Dose UVA Irradiation Induces Local Suppression of Contact Hypersensitivity, Langerhans Cell Depletion and Suppressor Cell Activation in C3H/HeJ Mice

Abstract— It has previously been demonstrated that chronic low-dose solar-simulated UV radiation could induce both local and systemic immunosuppression as well as tolerance to a topically applied hapten. In this study, we have used a chronic low-dose UV-irradiation protocol to investigate the effects of UVA on the skin immune system of C3H/HeJ mice. Irradiation with UVA+B significantly suppressed the local and systemic primary contact hypersensitivity (CHS) response to the hapten 2,4,6-trinitrochlo-robenzene. Furthermore UVA+B reduced Langerhans cell (LC) and dendritic epidermal T cell (DETC) densities in chronically UV-irradiated mice. Ultraviolet A irradiation induced local, but not systemic, immunosuppression and reduced LC (32%) but not DETC from the epidermis compared to the shaved control animals. Treatment of mice with both UVA+B and UVA radiation also induced an impaired secondary CHS response, and this tolerance was transferable with spleen cells. These results suggest that depletion of LC, but not DETC, may be involved in UVA-induced local immunosuppression in our model, and that tolerance was induced in the presence of normal numbers of DETC. Hence exposure of C3H/HeJ mice 5 days per week for 4 weeks with UVA can induce local immunosuppression and tolerance.     

LACK OF CORRELATION BETWEEN SUPPRESSION OF CONTACT HYPERSENSITIVITY BY UV RADIATION AND PHOTOISOMERIZATION OF EPIDERMAL UROCANIC ACID IN THE HAIRLESS MOUSE

Abstract The immunological consequences of exposure to UVA (320–400 nm) radiation are unclear. This study describes the relationship between the generation of epidermal cis -urocanic acid and the ability to respond to a contact-sensitizing agent, in hairless mice exposed to different UV radiation sources, which incorporate successively greater short-wavelength cutoff by filtration of the radiation from fluorescent UV tubes. Mice were exposed to these radiation sources at doses systematically varying in UVB radiation content but supplying increasing proportions of UVA radiation. All radiation sources were found to generate approximately 35% cis -urocanic acid in the epidermis, thus normalizing the sources for cis -urocanic acid production. However, only those sources richest in short-wavelength UVB resulted in suppression of the systemic contact hypersensitivity response. These sources also induced the greatest erythema reaction, measured as its edema component, in the exposed skin. A strong correlation was thus demonstrated between the induction of edema and the suppression of contact hypersensitivity, but there appeared to be no correlation between the generation of epidermal cis-urocanic acid and suppression of contact hypersensitivity. The sources richest in UVA content did not result in suppression of contact hypersensitivity: furthermore mice previously irradiated with such UVA-rich sources were refractory to the immunosuppressive action of exogenous cis-urocanic acid. A protective effect of the increased UVA content thus appeared to be inhibiting immunosuppression by the available endogenously generated or exogenously applied cⁱs-urocanic acid.     

Suppression of Delayed and Contact Hypersensitivity Responses in Mice Have Different UV Dose Responses

Although acute exposure to UV radiation suppresses the induction of delayed-type (DTH) and contact (CHS) hypersensitivity in mice, it is not clear whether the photo-biological mechanism(s) involved in suppressing these closely related immune reactions is the same. A careful examination of the UV dose responses and wavelength dependencies involved in suppressing CHS and DTH may provide important insights into the mechanisms involved. We compared the UV dose-response curves for suppressing four closely related immune reactions, local and systemic suppression of CHS to dinitrofluorobenzene, systemic suppression of DTH to Candida albicans and systemic suppression of DTH to alloantigen using three different UV spectra (FS40 sunlamps, Kodacel-filtered FS40 sunlamps and solar-simulated light). For each immune response studied, the amount of UVB radiation required to induce 50% immune suppression was lowest when FS40 sunlamps were used, highest with solar-simulated light and intermediate when Kodacel-filtered FS40 sunlamps were used, but the differences observed were not statistically significant. The UV dose-response curves for immune suppression differed significantly depending on the assay used, the site of antigenic sensitization and the antigen used. These findings suggest that the mechanisms by which UV radiation induces immune suppression differ for the four immunological reactions studied.     

Protection of UV-induced Suppression of Skin Contact Hypersensitivity: A Common Feature of Flavonoids after Oral Administration?

In this study we investigated the effect of the dietary ingredients fruit and vegetable, green tea phenol extract (GTP) and the specific flavonoid components quercetin and chrysin on the UV-induced suppression of the con-tact hypersensitivity (CHS) response to picryl chloride (PCl). The SKH-1 mice were fed with test diet from 2 or 4 weeks before and during the UV irradiation (daily, 95 mJ/cm²) and tested for the CHS ear-swelling response 10 weeks after the onset of the irradiation. For the CHS, mice were immunized with PCl by epicutaneous application on nonirradiated sites. Four days after sensitization all mice were challenged on both sides of each ear by topical application of one drop PCl. In addition, from mice fed with the fruit and vegetable mixture the number of Langerhans cells (LC) were scored in the skin and from mice fed with quercetin, quercetin levels in plasma were measured at week 11 after the start of UV irradiation. It was found that fruit and vegetable (19% in the diet), GTP (0.1% and 0.01% in the drinking water), quercetin (1% in the diet) and chrysin (1% and 0.1% in the diet), prevented statistically significantly the UV-induced suppression of CHS to PCl. In the skin of mice fed with fruit and vegetables combined with UV irradiation the number of LC were comparable to the control mice, whereas the number of LC were significantly diminished in mice treated with UV only. This protective effect on the presence of LC in the epidermis after UV irradiation, which was also observed in a previous study with quercetin, may play a role in the prevention of UV-induced immunosuppression by the flavonoids tested. In conclusion, we found protection of flavonoids against UV-induced effects on CHS, which may be a common feature of most flavonoids.